This is a huge problem, the success of the lockdown was on a scale that even the government didn't expect, and people are now fearful of returning to work and school because they've essentially been told that if you walk outside you'll essentially drop dead. The messaging needs to change, but managing to convince a public that you've feared into obeying a temporary measure too effectively that the risk is minimal whilst still announcing daily deaths 100+ will arguably be a tougher challenge than introducing the lockdown in the first place.
That will have the upside that it's unlikely any loosening will cause a "big bang" of people suddenly all over the streets. It might in lads in their 20s, but they're so low risk that it might not even matter unless they (as per one of the adverts) live with their Nan or something. (I think fear of giving it to your Nan is a very useful thing to remain in place - and maybe that's the way the promotion needs to go).
Re the lockdown I think they were expecting roughly 60% compliance and weren't expecting a load of businesses which can still legally open to voluntarily close - in particular the likes of Maccy's.